• David R Anderson, Michael J Dunbar, Eric R Bohm, Etienne Belzile, Susan R Kahn, David Zukor, William Fisher, Wade Gofton, Peter Gross, Stephane Pelet, Mark Crowther, Steven MacDonald, Paul Kim, Susan Pleasance, Nicki Davis, Pantelis Andreou, Philip Wells, Michael Kovacs, Marc A Rodger, Tim Ramsay, Marc Carrier, and Pascal-Andre Vendittoli.
• Dalhousie University, Halifax, Nova Scotia, Canada. david.anderson@cdha.nshealth.ca
• Ann. Intern. Med. 2013 Jun 4;158(11):800-6.

BackgroundThe role of aspirin in thromboprophylaxis after total hip arthroplasty (THA) is controversial.ObjectiveTo compare extended prophylaxis with aspirin and dalteparin for prevention of symptomatic venous thromboembolism (VTE) after THA.DesignMulticenter randomized, controlled trial with a noninferiority design based on a minimal clinically important difference of 2.0%. Randomization was electronically generated; patients were assigned to a treatment group through a Web-based program. Patients, physicians, study coordinators, health care team members, outcome adjudicators, and data analysts were blinded to interventions. (Current Controlled Trials: ISRCTN11902170).Setting12 tertiary care orthopedic referral centers in Canada.Patients778 patients who had elective unilateral THA between 2007 and 2010.InterventionAfter an initial 10 days of dalteparin prophylaxis after elective THA, patients were randomly assigned to 28 days of dalteparin (n = 400) or aspirin (n = 386).MeasurementsSymptomatic VTE confirmed by objective testing (primary efficacy outcome) and bleeding.ResultsFive of 398 patients (1.3%) randomly assigned to dalteparin and 1 of 380 (0.3%) randomly assigned to aspirin had VTE (absolute difference, 1.0 percentage point [95% CI, -0.5 to 2.5 percentage points]). Aspirin was noninferior (P < 0.001) but not superior (P = 0.22) to dalteparin. Clinically significant bleeding occurred in 5 patients (1.3%) receiving dalteparin and 2 (0.5%) receiving aspirin. The absolute between-group difference in a composite of all VTE and clinically significant bleeding events was 1.7 percentage points (CI, -0.3 to 3.8 percentage points; P = 0.091) in favor of aspirin.LimitationThe study was halted prematurely because of difficulty with patient recruitment.ConclusionExtended prophylaxis for 28 days with aspirin was noninferior to and as safe as dalteparin for the prevention of VTE after THA in patients who initially received dalteparin for 10 days. Given its low cost and greater convenience, aspirin may be considered a reasonable alternative for extended thromboprophylaxis after THA.Primary Funding SourceCanadian Institutes of Health Research.

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